Hydrocarbonylation has become an important and versatile approach to the synthesis of organic compounds and is commercially important for the synthesis of aldehydes. The reaction is based on the old OXO reaction which is the addition of a carbonyl group at an unsaturated bond in an olefin.
The most important industrial hydrocarbonylation reaction is hydroformylation which is the addition of formaldehyde to an olefin, resulting typically in an aldehyde. This reaction has been studied widely, and is regarded as a generalized procedure for aldehyde synthesis. Although hydroformylation can proceed stoichiometrically, the favored commerical reaction if catalytic.
Carbonylation reactions appear to be attractive for ketone synthesis, but the hydroformylation reaction fails for generalized ketone synthesis. In exceptional cases, ketones can be formed either stoichiometrically or catalytically by hydroformylation. Diethyl ketone forms readily by carbonylation of ethylene, although it competes in yield with propionaldehyde. Dibutyl ketone can be synthesized by carbonylation, though not as effectively. Other ketone synthesis reactions are rare or very specialized. Those that exist, it will be noted, form symmetrical ketones.
The catalysts used in hydroformylation reactions are normally cobalt or rhodium compounds although a host of metal complexes have been used. Rhodium catalysts are the newest, and are often the most selective for a preferred end product.
Nearly all the significant carbonylation reactions to date have involved hydroformylation. Although, in principle, higher order carbonylation, i.e., hydroacylation, appears an attractive possibility, efforts to obtain that reaction have been largely unsuccessful, and in particular, a general synthesis of unsymmetrical ketones by a carbonylation route which is catalytic in a metal compound has not been reported.